javascript - 将 Firebase 可观察到的 Angular 映射到模板

Question

我无法使用 Angular 迭代 Firebase 可观察对象以仅接收用户订单历史记录并将其输出到模板。我已经将 switchMap 更改为 map 以消除错误，但我似乎无法像以前那样访问模板中的数据......我是新手。请在下面找到所有必要的文件和数据库结构。

这段代码...

 this.orders$ = authService.user$.switchMap(u => orderService.getOrdersByUser(u.uid));

...给我这个错误...

Argument of type '(u: User) => Query' is not assignable to parameter of type '(value: User, index: number) => ObservableInput<{}>'.
  Type 'Query' is not assignable to type 'ObservableInput<{}>'.
    Type 'Query' is not assignable to type 'ArrayLike<{}>'.
      Property 'length' is missing in type 'Query'.

...我完全不知所措。如果您有任何建议，我将不胜感激。谢谢!

这是我的组件文件:

import { AuthService } from './../auth.service';
import { OrderService } from './../order.service';
import { Component, OnInit } from '@angular/core';
import 'rxjs/add/operator/switchMap';

@Component({
    selector: 'app-my-orders',
    templateUrl: './my-orders.component.html',
    styleUrls: ['./my-orders.component.css']
})
export class MyOrdersComponent {
    orders$;

    constructor(
        private authService: AuthService,
        private orderService: OrderService) {

        this.orders$ = authService.user$.switchMap(u => orderService.getOrdersByUser(u.uid));
        console.log(this.orders$);
    }
}

服务文件:

import { AngularFireDatabase } from 'angularfire2/database-deprecated';
import { Injectable } from '@angular/core';
import { CartService } from './cart.service';

@Injectable()
export class OrderService {
    constructor(
        private db: AngularFireDatabase,
        private cartService: CartService
    ) { }
    getOrdersByUser(userId: string) {
        return this.db.list('/orders').$ref.orderByChild('userId').equalTo(userId);
    }

}

和标记:

<h1>Orders</h1>
<table class="table">
    <thead>
        <tr>
            <th>Customer</th>
            <th>Date</th>
            <th></th>
        </tr>
    </thead>
    <tbody>
        <tr *ngFor="let order of orders$ | async">
            <td>{{ order.shipping.name }}</td>
            <td>{{ order.datePlaced | date}}</td>
            <td>
                <a href="#">View</a>
            </td>
        </tr>
    </tbody>
</table>

Answer 1

查询只能通过一种方法排序。这意味着您只能指定 orderByChild、orderByKey、orderByPriority 或 orderByValue。

如果你想使用动态查询:https://github.com/angular/angularfire2/blob/master/docs/rtdb/querying-lists.md

从您的服务文件中删除 equalTo 查询。

服务文件:

 import { AngularFireDatabase } from 'angularfire2/database-deprecated';
 import { Injectable } from '@angular/core';
 import { CartService } from './cart.service';

  @Injectable()
   export class OrderService {
    constructor(
     private db: AngularFireDatabase,
     private cartService: CartService
 ) { }
   getOrdersByUser(userId: string) {
    return 
 this.db.list('/orders').$ref.orderByChild('userId');
}